option optcr=0;

Sets
	i   /i1 * i20/
alias (j,i);

parameters
	c(i,j) cost 
	t(i,j)
	b;
c(i,j) = uniform(0,10);
t(i,j) = uniform(0,10);
b = 100;

variables
	z
	x(i,j);

binary variable x;

equations
	obj          objective
	inflow(i)
	outflow(j)
	kp;

obj..          z =e= sum( (i,j), c(i,j) * x(i,j) );
inflow(i)..    1 =e= sum( j, x(i, j) );
outflow(j)..   1 =e= sum( i, x(i, j) );
kp..           sum( (i,j), c(i,j) * x(i,j) ) =l= b;

model flow /obj, inflow, outflow, kp/;
solve flow using mip maximizing z;

parameter lambda(i);
variable bound1;

equation LR1 lagrangaian relaxation 1;
LR1.. bound1 =e= ;
model 